New Constraints on the Continuum Emission Mechanism of Active Galactic Nuclei: Intensive Monitoring of NGC 7469 in the X‐Ray and Ultraviolet (original) (raw)
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Short-term variabilities in X-ray/Optical/UV emission from Seyfert 1 galaxy NGC 4593
Bulletin de la Société Royale des Sciences de Liège, 2019
We present results obtained from a detailed multi-band analysis of the Seyfert 1 galaxy NGC 4593. Publicly available Swift monitoring observations in optical, ultraviolet and X-ray bands were used in the present work. A total of 185 pointings over a duration of about a month were used to understand the variabilities in emission in optical, ultraviolet, soft and hard X-ray bands. It was found that the source emission in the hard X-ray band (1.5-10 keV range) was highly variable compared to that at longer wavelengths. The variability amplitude decreased gradually from hard X-ray to optical bands. A cross-correlation analysis between light curves in different bands inferred that the observed variation in ultraviolet and optical bands is strongly correlated with the hard X-ray emission. Observed time lag for changes in emission in longer wavelength bands with respect to the hard X-ray emission suggests X-ray reprocessing as the cause of variation. Though the observed lag spectrum follow...
The Astrophysical Journal, 2000
From 1996 June 10 to 1996 July 29 the International AGN Watch monitored the Seyfert 1 galaxy NGC 7469 using the International Ultraviolet Explorer, the Rossi X-ray Timing Explorer and a network of ground-based observatories. On 1996 June 18, in the midst of this intensive monitoring period, we obtained a high signal-tonoise snapshot of the UV spectrum from 1150-3300 Å using the Faint Object Spectrograph on the Hubble Space Telescope. This spectrum allows us to disentangle the UV continuum more accurately from the broad wings of the emission lines, to identify clean continuum windows free of contaminating emission and absorption, and to deblend line complexes such as Lyα+N V, C IV+He II+O III], Si III]+C III], and Mg II+Fe II. Using the FOS spectrum as a template, we have fit and extracted line and continuum fluxes from the IUE monitoring data. The cleaner continuum extractions confirm the discovery of time delays between the different UV continuum bands by Wanders et al. Our new measurements show delays increasing with wavelength for continuum bands centered at 1485 Å, 1740 Å and 1825 Å relative to 1315 Å with delays of 0.09, 0.28 and 0.36 days, respectively. Like many other Seyfert 1 galaxies, the UV spectrum of NGC 7469 shows intrinsic, blue-shifted absorption in Lyα, N V and C IV. Soft X-ray absorption is also visible in archival ASCA X-ray spectra. The strength of the UV absorption, however, is not compatible with a single-zone model in which the same material absorbs both the UV and Xray light. Similar to other Seyfert galaxies such as NGC 3516, the UV-absorbing gas in NGC 7469 has a lower ionization parameter and column density than the X-ray absorbing material. While the UV and X-ray absorption does not arise in the same material, the frequent occurrence of both associated UV absorption and X-ray warm absorbers in the same galaxies suggests that the gas supply for each has a common origin.
Evidence for variability time-scale-dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469
Monthly Notices of the Royal Astronomical Society, 2020
Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825...
Modeling the X‐Ray–Ultraviolet Correlations in NGC 7469
The Astrophysical Journal, 2000
We model the correlated X-rayÈUV observations of NGC 7469, for which well-sampled data in both these bands have recently been obtained in a multiwavelength monitoring campaign. To this end, we derive the transfer function in wavelength j and time lag q for reprocessing hard (X-ray) photons from a point source to softer ones (UVÈoptical) by an inÐnite plane (representing a cool, thin accretion disk) located at a given distance below the X-ray source, under the assumption that the X-ray Ñux is absorbed and emitted locally by the disk as a blackbody of temperature appropriate to the incident Ñux. Using the observed X-ray light curve as input, we have computed the expected continuum UV emission as a function of time at several wavelengths (1315, 6962, 15000, and 30000 assuming that the X-ray source is A), located one Schwarzschild radius above the disk plane, with the mass of the black hole M and the latitude angle h of the observer relative to the disk plane as free parameters. We have searched the parameter space of black hole masses and observer azimuthal angles, but we were unable to reproduce UV light curves that would resemble, even remotely, those observed. We also explored whether particular combinations of the values of these parameters could lead to light curves whose statistical properties (i.e., the autocorrelation and cross-correlation functions) would match those corresponding to the observed UV light curve at 1315 Even though we considered black hole masses as large as 109 no such A. M _ , match was possible. Our results indicate that some of the fundamental assumptions of this model will have to be modiÐed to obtain even approximate agreement between the observed and model X-rayÈUV light curves.
The origin of the x-ray and ultraviolet emission in ngc 7469
The Astrophysical …, 2000
We present a spectral analysis of a ∼ 30 d, near-continuous observation of the Seyfert 1 galaxy NGC 7469 with RXTE. Daily integrations show strong spectral changes during the observation. Our main result is that we find the X-ray spectral index to be correlated with the UV flux. Furthermore, the broad-band X-ray photon flux is also correlated with the UV continuum. These correlations point towards a model in which the X-rays originate via thermal Comptonization of UV seed photons. Furthermore, the UV is also correlated with the extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data analysis therefore re-opens the possibility the the UV photons and their variability arise from reprocessing, as long as the primary source of heating is photo-electric absorption in the reprocessor, rather than Compton downscattering, A coherent picture of the X-ray/UV variability can therefore be constructed whereby absorption and reprocessing of EUV/soft X-rays in a standard accretion disk produce a variable seed photon distribution which are in turn up-scattered into the X-ray band. We also find a significant correlation between the 2-10 keV flux and the 6.4 keV iron Kα line suggesting that at least some portion of the line originates within ∼ 1 lt day of the X-ray continuum source. Neither the power law photon index nor the Compton reflection component are correlated with the 2-10 keV flux. The latter is not correlated -2with the iron Kα line flux either. We do find an apparent correlation between the X-ray spectral index and the strength of the Compton reflection component. In an Appendix we show, however, that this can be produced by a combination of statistical and systematic errors. We conclude the apparent variations in the Compton reflection component may be an artifact of these effects.
Variability and the X-ray/UV ratio of active galactic nuclei
Astronomy & Astrophysics, 2013
Context. The observed relation between the X-ray radiation from active galactic nuclei, originating in the corona, and the optical/UV radiation from the disk is usually described by the anticorrelation between the UV to X-ray slope α ox and the UV luminosity. Many factors can affect this relation, including: i) enhanced X-ray emission associated with the jets of radio-loud AGNs, ii) X-ray absorption associated with the UV broad absorption line (BAL) outflows, iii) other X-ray absorption not associated with BALs, iv) intrinsic X-ray weakness, v) UV and X-ray variability, and non-simultaneity of UV and X-ray observations. The separation of these effects provides information about the intrinsic α ox − L UV relation and its dispersion, constraining models of disk-corona coupling. Aims. We use simultaneous UV/X-ray observations to remove the influence of non-simultaneous measurements from the α ox − L UV relation. Methods. We extract simultaneous data from the second XMM-Newton serendipitous source catalogue (XMMSSC) and the XMM-Newton Optical Monitor Serendipitous UV Source Survey catalogue (XMMOMSUSS), and derive the single-epoch α ox indices. We use ensemble structure functions to analyse multi-epoch data.
X-Ray Spectral Variability in NGC 7469
The Astrophysical Journal, 1996
We present analyses of two Ginga observations and two observations from the ROSAT database o NGC 7469, focusing on the spectral variability observed on timescales of days and longer. During the day 1988 Ginga observation, the hardness ratio (8-21 keV/3.4-5.7 keV) increased significantly as th, total flux decreased by 30%. As the spectrum is well fit by the reflection model and since the spectra variability dominates the higher energy band, this could be explained by either a variation in the power law index or in the effective covering fraction of the reflecting material. This ambiguity is inherent i_ reflection modeling of Ginga spectra from moderate flux Seyfert 1 galaxies. Assuming that the power-lax index did not change, we find that the reflected flux is consistent with being constant, suggesting tha much of the reflecting material may be located more than 3 light-days from the continuum source wit] the molecular torus being a plausible site. This scenario is also supported by the report of a narrox' rather than broad iron K_ line in the ASCA data by Guainazzi et al. NGC 7469 was faint during th, 1989 Ginga observation, but variability was observed with doubling timescale of 5 hr, and the spectrun was harder. A reflection component could not be constrained, and the change in the spectrum could b explained by an increase in neutral absorption. The brighter of two ROSAT spectra was significantly softer, and in both spectra there was evidence c spectral complexity, as has been previously reported by Turner, George, & Mushotzky and Brandt et a! The spectrum could be fit by a variety of two-component models, including a warm absorber model, a_ ionized disk model, and a thermal model with single-component blackbody spectrum, but joint fitting c the 1988 average Ginga spectrum and the nonsimultaneous ROSAT spectra favored thermal models, a other models required an anomalously high reflection ratio. This model is supported by the observatio: of a soft excess component and the lack of ionized absorption edges in the ASCA spectrum by Guain azzi et al. The long-term spectral variability could be explained b)' relative variability between th power-law and soft excess component normalizations, perhaps implying that hard X-ray reprocessing i: thermal material does not dominate on long timescales.
Astrophysical Journal Supplement Series, 1997
We present the final installment of an intensive 13 year study of variations of the optical continuum and broad H emission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 H measurements. The H variations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r / L 1=2 ion . Moreover, the apparently linear nature of the correlation between the H response time and the nonstellar optical continuum F opt arises as a consequence of the changing shape of the continuum as it varies, specifically F opt / F 0:56 UV .
X-ray/UV variability of narrow-line Seyfert 1 galaxies
2015
Narrow-line Seyfert 1 galaxies (NLS1s) host low black hole masses ( MBH . 10M⊙) and are accreting at high accretion rates. These properties make NLS1s ideal AGN to study the coupling betwee n th accretion disks and hot corona by studying UV and X-ray variabi l ty. Here we present UV and X-ray variability of the NLS1 1H 0707–495 whic h s well known for its relativistically broadened iron K and L lines. We found no obvious correlation between the UV and X-ray emission on lig ht-crossing time, implying absence of significant reprocessed emission . The lack of reprocessing is most likely due to the strong bending of X-ra y emission from a compact corona onto the innermost regions, giving ris e to broadened iron lines but no illumination onto the intermediate /outer disk where reprocessed UV emission is expected. We also found X-ray spectral va i bility – spectral steepening with increasing X-ray flux, which canno t be due to the variations in the seed flux as the UV emission is not corr...